Working on some OSM styling I've found that nowadays OSM uses mostly
SVG based icons.
The icons are "black", but the CartoCSS style associates them with a color, e.g.:
So ok, I set up to make an equivalent, by creating a SVG based mark factory,
work in progress here:
The extraction of shapes turned out to be not too hard, as I could reuse work off the
SVGExternalGraphicFactory. The annoying bit is handling the relative paths, which
is a new concept in WellKnownName.
I looked at a few approaches, including SE 1.1 ExternalMark, and eventually settled
down on adding an explicit file reference, like this:
which, starting from a black, 14x14 SVG symbol, results in a 32x32 red icon:
The magic is done, as usual, in SLDParser, and would have to be replicated in the gt-xsd bindings and
inside GeoServer (the data dir handling code).
 Discarded because we want the entire thing, not a bit inside of a library, and there is no way to write SE 1.1, so it would be unusable for CSS/Mapbox/YSLD